I made my own trolley, all I can say is to use a drillbit SMALLER than the bolt that will be going through it. I dab silicone seal on after drilling the small hole, then thread/screw the Stainless bolt through the guide hole, dab a bit of silicone inside, then attach the Stainless washer and nut. The Silicone acts as a bit of lubricant and a thread sealer too.

I installed mine last night and as far as I can tell, it came out good. The drill bits I used (along with my notes) are at home so I'm not going to try to remember what I used. If I remember, I'll post up when I go home for lunch. It's scary drilling holes in these beautiful boats.